Problem: Umaima was assigned problems 48 through 68 for homework tonight. If Umaima did all of the problems she was assigned, how many problems did she do?
Answer: Instead of counting problems 48 through 68, we can subtract 47 from each number so we instead consider problems 1 through 21. We see that Umaima did 21 problems. Notice that she did 21 and not 20 problems.